1. Field of the Invention
The invention is directed to a method for introducing and metering a liquid treatment medium into the waste gas flow in combustion processes. The invention is also directed to an atomizing nozzle, particularly for implementing the method.
2. Description of the Prior Art
In order to introduce a treatment medium, e.g. chemicals for reducing the NO.sub.x content in waste gases, it is known to atomize the chemicals by means of a carrier medium in a two-component nozzle and thus introduce it into the combustion chamber. However, the two-component nozzle has the disadvantage that steam or compressed air is supplied as atomizing medium or carrier medium, so that an unwanted dilution of the flue gases with air or steam occurs, which reduces the efficiency of the steam production or, in some cases, of the waste gas cleaning system because a large quantity of this medium is required for the atomization. The atomization in a two-component nozzle is effected by means of kinetic energy of the atomizing medium, which causes the high throughput of this medium. Moreover, these atomizing media are expensive, since they require increasingly high amounts of energy and, in the event that steam is applied, prepared evaporator feed water. The guidance of these media through lines until the individual nozzles proves costly, since either thermally insulated pipes must be used in the case of steam or relatively large cross sections must be used for reducing the pressure loss in the system. The expansion of the media at the nozzle outlet and the media flow in the lines generate a relatively high noise level which often even necessitates soundproofing.
A method and an atomizing nozzle for admixing an atomized liquid into a gas flow is known from DE-OS 35 41 599, in which the atomized liquid, together with the atomizing gas, is divided into a plurality of partial flows, wherein every partial flow has a component in the same direction as that of the gas flow in which the atomized liquid is to be introduced. In this method, by means of a two-component nozzle comprising two concentric pipes, the liquid to be atomized is guided in the inner pipe and the atomization gas is guided in the outer pipe, which atomization gas atomizes the liquid at the opening of the inner pipe. In so doing, the atomized liquid is first introduced into a distributor chamber from which a plurality of pipes proceed diagonally relative to the flow direction of the gas flow so that the waste gas flow to be treated can flow around the outlet openings of these distributor pipes on all sides in order to prevent the atomized liquid from being baked on at the outlet end of the pipes. In a simple two-component nozzle, in which the atomized liquid emerges in the flow direction of the gas flow to be treated, the atomized liquid can settle at the outlet opening of the two-component nozzle because of the turbulence at the latter. In addition to the disadvantages already discussed above with respect to a two-component nozzle, this known two-component nozzle also has the disadvantage that the metering of the liquid to be atomized presents difficulties, since the pipe of the two-component nozzle for conveying the liquid to be atomized has a determined delivery capacity and this quantity can not be throttled too sharply because, otherwise, a uniform atomization of the liquid does not occur.